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File System Module

ElenixOS uses a unified path format, namely POSIX-style paths. All file operations must go through the storage service, and the system cannot directly access the underlying file system.

LVGL File System Integration​

The LVGL file system driver works as an adapter layer:

  • Intercepts all LVGL file operations
  • Translates them into eos_service_storage API calls
  • Ensures all file access goes through the ElenixOS storage sandbox

Architecture​

LVGL → FS driver → eos_service_storage → eos_fs_port

Why LV_FS_DEFAULT_DRIVE_LETTER Must Be Fixed?​

LVGL uses a "drive letter" mechanism (e.g. 'S:/path') to select file system drivers. If a path does not contain a drive letter, LVGL falls back to LV_FS_DEFAULT_DRIVE_LETTER.

In ElenixOS:

  • A single unified file system is exposed to applications
  • All paths should be POSIX-style (e.g. "/data/config.json")
  • The LVGL driver internally handles drive letter translation

Therefore, LV_FS_DEFAULT_DRIVE_LETTER must point to the ElenixOS driver, otherwise LVGL may route file operations to an unexpected backend.

#if LV_FS_DEFAULT_DRIVE_LETTER != EOS_LVGL_FS_LETTER
#error "LV_FS_DEFAULT_DRIVE_LETTER must match EOS_LVGL_FS_LETTER"
#endif

Path Handling​

Path Sanitization​

The _storage_sanitize_path function ensures all paths have the EOS_SYS_ROOT_DIR prefix:

  • If the path already contains the system root directory prefix, it remains unchanged
  • If the path starts with "/" (absolute path), the system root directory prefix is added
  • If the path is a relative path, the system root directory prefix is added

JSON Storage API​

The storage service provides a complete set of JSON file operation interfaces for reading and modifying JSON format configuration files.

Load JSON File​

Load a JSON file from storage:

cJSON *eos_storage_json_load(const char *path);

Returns a cJSON root object, or NULL on failure.

Save JSON File​

Save a cJSON object to a file:

eos_result_t eos_storage_json_save(const char *path, cJSON *root);

Boolean Operations​

bool eos_storage_json_get_bool(const char *path, const char *key, bool default_value);
eos_result_t eos_storage_json_set_bool(const char *path, const char *key, bool value);

String Operations​

char *eos_storage_json_get_string(const char *path, const char *key, const char *default_value);
eos_result_t eos_storage_json_set_string(const char *path, const char *key, const char *value);

The returned string needs to be freed using eos_free after use.

Number Operations​

double eos_storage_json_get_number(const char *path, const char *key, double default_value);
eos_result_t eos_storage_json_set_number(const char *path, const char *key, double value);

JSON Object Operations​

cJSON *eos_storage_json_get_json(const char *path, const char *key);
eos_result_t eos_storage_json_set_json(const char *path, const char *key, cJSON *json_value);

The returned cJSON object needs to be freed using cJSON_Delete after use.

Create JSON File​

Creates a JSON file with default content if the file does not exist:

eos_result_t eos_storage_json_create_if_not_exist(const char *path, const char *default_json);

File System Operations​

Check File Type​

bool eos_storage_is_dir(const char *path);
bool eos_storage_is_file(const char *path);
bool eos_storage_is_valid_filename(const char *name);

Write to File​

Write a string to a file (automatically adds newline at the end):

eos_result_t eos_storage_puts(const char *s, eos_file_t fp);

Create Directory​

Creates the directory if it does not exist:

eos_result_t eos_storage_mkdir_if_not_exist(const char *path);

Recursively create directory tree:

eos_result_t eos_storage_mkdir_recursive(const char *path);

Create File​

Creates a file with default content if it does not exist:

eos_result_t eos_storage_create_file_if_not_exist(const char *path, const char *default_content);

Read File​

Read entire file content into dynamically allocated buffer (can only read text files):

char *eos_storage_read_file(const char *path);

Returns a dynamically allocated buffer that needs to be freed using eos_free after use.

Write File​

eos_result_t eos_storage_write_file(const char *path, const void *data, size_t data_size);

Immediate Write (Bypass Deferred Writer)​

eos_result_t eos_storage_write_file_immediate(const char *path, const void *data, size_t data_size);
char *eos_storage_read_file_immediate(const char *path);

Deferred File Writer (DFW)​

The Deferred File Writer is used for batch writing files, reducing frequent Flash write operations to extend Flash lifespan.

How It Works​

  • When writing data, it first writes to the buffer
  • When eos_dfw_sync() is called, buffer data is synchronized to the file system

Sync Buffer to File System​

void eos_dfw_sync(void);

Write Data​

bool eos_dfw_write(const char *path, const uint8_t *data, size_t data_size);

Returns true if the task has been added to the queue and will be written to the file when eos_dfw_sync() is called next time.

Read File Data​

uint8_t *eos_dfw_read(const char *path);

Returns file content on success, NULL on failure. The returned pointer needs to be freed manually.

Initialize​

void eos_dfw_init(void);

LVGL File System Registration​

Register the LVGL file system driver, routing all file operations to the ElenixOS storage service:

void eos_lvgl_fs_register(void);